Radiation image pick-up device and method therefor, and radiation image pick-up system

ABSTRACT

Sensitivity is freely changeable to another one in correspondence to a photographing mode, and both still image photographing and moving image photographing for example which are largely different from each other in dosage of exposure to radiation and which are also different from each other in required sensitivity are carried out so as to meet that request. A source or drain electrode of a TFT  21  is connected to a signal output circuit  3  through a signal line  14   a  and an IC  5 . A source/drain of a TFT  23  is connected to the signal output circuit  3  through a signal line  14   b  and the IC  5 . Thus, in each pixel  6 , any one of the signal lines  14   a  and  14   b  is freely selectable when a signal is read out.

RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/576,349,filed Apr. 18, 2006, claims benefit of that application under 35 U.S.C.§120, and claims benefit under 35 U.S.C. §119 of Japanese patentapplications nos. 2003-392725, filed Nov. 21, 2003, and 2004-207273,filed Jul. 14, 2004. The entire disclosure of each of the threementioned prior applications is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a radiation image pick-up device andmethod for photographing an image of incident radiation, and a radiationimage pick-up system, and is applied to a medical image diagnosisapparatus, a non-destructive inspection apparatus, and an analyzer usingradiation. Note that, it is supposed that in this specification, anelectromagnetic wave such as visible light, X-rays, as well as (α-rays,β-rays, γ-rays, and the like are also included within the broad scope ofthe term “radiation”.

BACKGROUND ART

Recent advances in the liquid crystal panel manufacturing techniquesusing thin film transistors (TFTs), and utilization of an area serverhaving a semiconductor conversion element in various fields (e.g., inthe field of a medical X-ray image pick-up device), have enabledincreased surface area and digitization for medical radiation imagepick-up devices as well. The medical radiation image pick-up device,unlike a liquid crystal panel and the like, has a feature in that aminute signal is digitized to output a corresponding image, and hencecan photograph an image of radiation instantaneously to display thephotographed image on a display device in an instant. At the presenttime, as for such a radiation image pick-up device, one for still imagephotographing has been commercialized.

FIG. 11 is a schematic plan view schematically showing an example of aconventional radiation image pick-up device, FIG. 12 is an equivalentcircuit diagram of the conventional radiation image pick-up device shownin FIG. 11, and FIG. 13 is an equivalent circuit diagram of one pixeland a signal reading circuit in the conventional radiation image pick-updevice shown in FIG. 11 (refer to JP 8-116044 A for example).Hereinafter, a case where an image of X-ray as radiation is photographedwill be described.

As shown in FIG. 11, the conventional radiation image pick-up deviceincludes a sensor substrate 101 in which a plurality of pixels eachhaving a photoelectric conversion function are disposed, a scanningcircuit 102 for scanning the pixels, a signal output circuit 103 foroutputting signals from the pixels, ICs 104 through which the sensorsubstrate 101 and the scanning circuit 102 are connected to each other,and ICs 105 through which the sensor substrate 101 and the signal outputcircuit 103 are connected to each other.

As shown in FIG. 12, a plurality of pixels 106 are disposed in matrix inthe sensor substrate 101. Note that 3×4 pixels are illustrated in thepixel area for the sake of convenience in FIG. 12, in actuality, a largenumber of pixels, 1,000×2,000 pixels for example, are disposed therein.In addition, similarly, the illustration of ICs of the scanning circuitis omitted here for the sake of convenience.

As shown in FIGS. 12 and 13, each pixel 106 is constituted by aphotoelectric conversion element 111 as a semiconductor element forconverting incident X-rays into electric charges, and a thin filmtransistor (TFT) 112 acting as a switching element for reading out theresultant electric charges.

In each pixel 106, the photoelectric conversion element 111 is connectedto the signal output circuit 103 through a bias line 110 which is commonto all the pixels, and thus a constant bias voltage is applied from thesignal output circuit 103 to the photoelectric conversion element 111.In addition, in each pixel 106, a gate electrode of the TFT 112 isconnected to the scanning circuit 102 through the IC 104 (not shown) anda gate line 113 which is common to every row in the matrix. Thus, thescanning circuit 102 controls an operation (turn-ON/turn-OFF) of the TFT112. In addition, in each pixel 106, a source or drain electrode of theTFT 112 is connected to the signal output circuit 103 through the IC 105by way of a signal reading wiring (signal line) 114 which is common toevery column in the matrix.

As shown in FIGS. 12 and 13, the IC 105 includes an amplifier 115serving as a signal reading circuit. One input terminal of the amplifier115 is connected to the signal line 114, and the other input terminalthereof is connected to a power supply 116. Moreover, a gain switchingcircuit 117 having capacitors Cf1, Cf2, and Cf3 is connected to theamplifier 115, and thus a gain of the amplifier 115 can be switched overto another one through the combination of the capacitors Cf1, Cf2, andCf3.

Here, as shown in FIG. 13, a capacity of the photoelectric conversionelement 111 is assigned C1, a parasitic capacity of the signal line 114is assigned C2, and a capacity of the amplifier 115 is assigned Cf. AnX-ray applied to a subject for exposure is attenuated as it istransmitted through the subject to be wavelength-converted into visiblelight by a phosphor layer (wavelength conversion member)(not shown). Theresultant visible light is then made incident on the photoelectricconversion element 111 to be converted into electric charges Q.

Subsequently, upon turn-ON of the TFT 112, the gain of 1/Cf-fold is setin the amplifier 115. As a result, an output voltage Vout is expressedby Vout=−Q/Cf, and this voltage signal is then read out from the signaloutput circuit 103 to the outside. After completion of the operation forreading out the voltage signal Vout, the electric charges which aregenerated in the photoelectric conversion element 111 but remaineduntransferred are removed due to a change in electric potential of thecommon bias line 110.

However, the above-described conventional radiation image pick-up deviceprincipally aims at photographing a still image, and hence sensitivity(S/N ratio) is fixed at constant. Thus, the S/N ratio may becomeinsufficient depending on the photographing modes. That is, theconventional radiation image pick-up device involves a problem in thatit has little tolerance for differences in the attenuation of the X-raysbetween different subjects, or for large differences in the dosage ofexposure to the X-rays such as when still image photographing and movingimage photographing are performed.

DISCLOSURE OF THE INVENTION

In light of the foregoing, the present invention has been made in orderto solve the above-mentioned problems, and it is therefore an object ofthe present invention to provide an inexpensive and high-performanceradiation image pick-up device and a method therefor, and an inexpensiveand high-performance radiation image pick-up system which are capable offreely switching sensitivity over to another one in correspondence to asituation and an object of the image photographing to flexibly copetherewith, i.e., capable of carrying out both still image photographingand moving image photographing for example which are largely differentfrom each other in dosage of exposure to radiation and which are alsodifferent in required sensitivity so as to meet that request.

A radiation image pick-up device of the present invention includes: aplurality of pixels disposed in matrix, each of the pixels including atleast one photoelectric conversion element for converting incidentradiation into electric charges; and a signal output circuit foroutputting signals from the pixels, in which a plurality of signalreading wirings through which the pixel and the signal output circuitare connected to each other are provided for each pixel.

In further aspect of the radiation image pick-up device of the presentinvention, the photoelectric conversion element includes a wavelengthconversion member for performing wavelength conversion on incidentradiation.

In further aspect of the radiation image pick-up device of the presentinvention, each of the pixels includes semiconductor elements connectedto the signal reading wirings, and any one of the signal reading wiringsis freely selectable based on actuation of the semiconductor elements.

In further aspect of the radiation image pick-up device of the presentinvention, at least one of the semiconductor elements is a sourcefollower.

In further aspect of the radiation image pick-up device of the presentinvention, a signal reading circuit for reading out a signal from thepixel is provided to each of the signal reading wirings.

In further aspect of the radiation image pick-up device of the presentinvention, a signal reading circuit for reading out a signal from thepixel is provided in common to the signal reading wirings.

In further aspect of the radiation image pick-up device of the presentinvention, the two signal reading circuits are provided.

A radiation image pick-up method of the present invention includes usinga device which includes: a plurality of pixels disposed in matrix, eachof the pixels including at least one photoelectric conversion elementfor converting incident radiation into electric charges; and a signaloutput circuit for outputting signals from the pixels, in which any oneof a plurality of signal reading wirings which are provided for eachpixel and through which the corresponding pixel and the signal outputcircuit are connected to each other is selected in correspondence to aphotographing mode to be used.

In further aspect of the radiation image pick-up method of the presentinvention, the photoelectric conversion element performs wavelengthconversion on incident radiation, and converts the conversion resultsinto electric charges.

In further aspect of the radiation image pick-up method of the presentinvention, any one of the plurality of signal reading wirings isselected in correspondence to magnitude of a dosage of radiation.

In further aspect of the radiation image pick-up method of the presentinvention, each of the pixels includes semiconductor elements connectedto the plurality of signal reading wirings, and at least one of thesemiconductor elements is a source follower, and when in case of thephotographing mode involving a low dosage of radiation, the signalreading wiring having the source follower is selected.

A radiation image pick-up system of the present invention includes: aradiation image pick-up device; radiation generation means for applyingradiation; selection means for selecting any one of the plurality ofsignal reading wirings in the radiation image pick-up device incorrespondence to magnitude of a dosage of radiation; and control meansfor controlling the application of the radiation by the radiationgeneration means and drive of the radiation image pick-up device basedon the selection by the selection means.

In further aspect of the radiation image pick-up system of the presentinvention, there is further provided a photographing switch with whichany one of the plurality of signal reading wirings is freely selectablebased on an input by an operator, and the selection means selects anyone of the signal reading wirings based on input made with thephotographing switch.

In further aspect of the radiation image pick-up system of the presentinvention, the photographing switch is adapted to be switched ON into aplurality of strokes corresponding to the number of the signal readingwirings, and the respective strokes correspond to an increase in dosageof radiation in ascending order.

In light of the fact that the conventional radiation image pick-updevice aims principally at photographing a still image and thus thesensitivity (S/N ratio) is fixed at constant, the inventors of thepresent invention have earnestly carried out the examination in order toextend the sensitivity depending on the photographing modes (such asstill image photographing and moving image photographing). As a result,the inventors have hit upon such a device that a plurality of signalreading wirings (signal wirings) are distributed for each pixel, andsignal reading circuits and the like corresponding to the photographingmodes are provided for the signal wirings, respectively, to allow anyone of the signal wirings to be freely selectable.

More specifically, for example, two signal wirings are distributed foreach pixel, and one signal line is provided for the still imagephotographing. The still image photographing corresponds to thephotographing mode involving a high dosage of exposure to the radiation,and hence the required sensitivity is relatively low. Thus, there isadopted a configuration that the electric charge amplification is notcarried out within the pixel, but is carried out in the signal readingcircuit connected to the signal line concerned for example. On the otherhand, the other signal wiring is provided for the moving imagephotographing. The moving image photographing corresponds to the imagephotographing mode involving a low dosage of exposure to the radiation,and hence the required sensitivity is relatively high. Thus, there isadopted a configuration that the electric charge amplification iscarried out within the pixel to suppress generation of any of noises.

According to the present invention, there are realized the inexpensiveand high-performance radiation image pick-up device and radiation imagepick-up system which are capable of freely switching sensitivity over toanother one in correspondence to a situation and an object of the imagephotographing to flexibly cope therewith, i.e., capable of carrying outboth still image photographing and moving image photographing forexample which are largely different from each other in dosage ofexposure to radiation and which are also different in requiredsensitivity so as to meet that request.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a schematic plan view schematically showing an example of aradiation image pick-up device according to a first embodiment of thepresent invention;

FIG. 2 is an equivalent circuit diagram of the radiation image pick-updevice according to the first embodiment of the present invention;

FIG. 3 is an equivalent circuit diagram of one pixel and a signalreading circuit in the radiation image pick-up device according to thefirst embodiment of the present invention;

FIG. 4 is a schematic cross sectional view of a photoelectric conversionelement and a TFT in the radiation image pick-up device according to thefirst embodiment of the present invention;

FIG. 5 is a schematic plan view schematically showing a modification ofthe radiation image pick-up device according to the first embodiment ofthe present invention;

FIG. 6 is an equivalent circuit diagram of a radiation image pick-updevice according to a second embodiment of the present invention;

FIG. 7 is an equivalent circuit diagram of one pixel and a signalreading circuit in the radiation image pick-up device according to thesecond embodiment of the present invention;

FIG. 8 is a schematic view schematically showing an example of aradiation image pick-up system according to a third embodiment of thepresent invention;

FIG. 9 is a flow chart showing an operation of the radiation imagepick-up system according to the third embodiment of the presentinvention;

FIG. 10 is a timing chart explaining an image pick-up operation usingthe radiation image pick-up system according to the third embodiment ofthe present invention;

FIG. 11 is a schematic plan view schematically showing an example of aradiation image pick-up device according to a prior art;

FIG. 12 is an equivalent circuit diagram of the radiation image pick-updevice according to the prior art; and

FIG. 13 is an equivalent circuit diagram of one pixel and a signalreading circuit in the radiation image pick-up device according to theprior art.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will hereinafter be described indetail with reference to the accompanying drawings. A case where aphotograph of a subject is taken using X-rays as radiation will bedescribed herein.

First Embodiment

First of all, a first embodiment of the present invention willhereinafter be described.

FIG. 1 is a schematic plan view schematically showing an example of aradiation image pick-up device according to a first embodiment of thepresent invention.

FIG. 2 is an equivalent circuit diagram of the radiation image pick-updevice according to the first embodiment of the present invention, andFIG. 3 is an equivalent circuit diagram of one pixel and a signalreading circuit in the radiation image pick-up device according to thefirst embodiment of the present invention.

As shown in FIG. 1, the radiation image pick-up device includes a sensorsubstrate 1 in which a plurality of pixels each having a photoelectricconversion function are disposed, a scanning circuit 2 for scanning thepixels, a signal output circuit 3 for outputting signals from therespective pixels, ICs 4 through which the sensor substrate 1 and thescanning circuit 2 are connected to each other, and ICs 5 through whichthe sensor substrate 1 and the signal output circuit 3 are connected toeach other.

As shown in FIG. 2, a plurality of pixels 6 are disposed in matrix onthe sensor substrate 1. Note that while 3×3 pixels are illustrated in apixel area in FIG. 2 for the sake of convenience, in actuality, a largenumber of pixels, 1,000×2,000 pixels, for example, are disposed. Inaddition, similarly, the illustration of ICs of the scanning circuit isomitted here for the sake of convenience.

In this embodiment, as shown in FIGS. 2 and 3, each pixel 6 includes aphotoelectric conversion element 11 as a semiconductor element forconverting incident X-rays into electric charges, and semiconductorelements (switching elements) for reading out the resultant electriccharges. The switching elements include a thin film transistor (TFT) 21and a TFT 22 as a source follower which are provided so as to be freelyselectable.

In each pixel 6, the photoelectric conversion element 11 is connected tothe signal output circuit 3 through a bias line 12 which is common toall the pixels. Thus, a constant bias voltage is applied from the signaloutput circuit 3 to the photoelectric conversion element 11. Inaddition, two gate lines 13 a and 13 b which are common to every row inthe matrix are provided for each pixel 6. Here, a gate electrode of theTFT 21 is connected to the scanning circuit 2 through the gate line 13 aand a corresponding one of the ICs 4 (not shown), and a gate electrodeof the TFT 23 is connected to the scanning circuit 2 through the gateline 13 b and the corresponding one of the ICs 4 (not shown). Thus, thescanning circuit 2 controls operations (turn-ON/turn-OFF) of the TFTs 21and 23(22). Moreover, two signal reading wirings (signal lines) 14 a and14 b which are common to every column in the matrix are provided foreach pixel 6. Here, a source or drain electrode of the TFT 21 isconnected to the signal output circuit 3 through the signal line 14 aand corresponding one of the ICs 5, and a source or drain electrode ofthe TFT 22 is connected to the signal output circuit 3 through thesignal line 14 b and the corresponding one of the ICs 5. Thus, in eachpixel 6, any one of the signal lines 14 a and 14 b is freely selectablein reading out a signal therefrom.

As shown in FIGS. 2 and 3, each IC 5 includes an amplifier 15 a and TFTs24 and 25 which constitute the signal reading circuit, and an amplifier(operational amplifier) 15 b and TFTs 26 and 27 which constitute thesignal reading circuit. The amplifier 15 a and the TFTs 24 and 25 areconnected to the signal line 14 a, and the amplifier 15 b and the TFTs26 and 27 are connected to the signal line 14 b. Here, one inputterminal of the amplifier 15 a is connected to the signal line 14 a, andthe other input terminal thereof is connected to a power supply 16.Moreover, a gain switching circuit 17 including capacitors Cf1, Cf2, andCf3 is connected to the amplifier 15 a, and hence a gain of theamplifier 15 a can be switched over to another one through thecombination of the capacitors Cf1, Cf2, and Cf3. Further, a TFT 28 isconnected to an output terminal of the amplifier 15 a, and a TFT 29 isconnected to an output terminal of the amplifier 15 b so that a signalcan be outputted.

FIG. 4 is a schematic cross sectional view of the photoelectricconversion element 11 and the TFT 21 in the radiation image pick-updevice.

The photoelectric conversion element 11 and the TFT 21 are structured asfollows.

First of all, the TFT 21 will hereinafter be described.

A pattern of an electrode layer 202 that becomes a gate electrode isformed on a substrate 201, and an insulating layer 203 is deposited onthe substrate 201 so as to cover the electrode layer 202. A pattern of asemiconductor layer 204 made of silicon or the like is formed on theinsulating layer 203. Impurity ions are implanted at high concentrationinto both side portions of the semiconductor layer 204 to form a pair ofimpurity diffusion layers 205 and 206 that become a source and a drain.Patterns of electrode layers 207 and 208 that becomes source and drainelectrodes are formed in patterns so as to be connected to the impuritydiffusion layers 205 and 206, respectively, thereby structuring the TFT21.

Next, the photoelectric conversion element 11 will hereinafter bedescribed.

An insulating layer 209 is deposited over the entire surface includingupper surfaces of the electrode layers 202, 207, and 208. A pattern of asemiconductor layer 210 made of silicon or the like is formed on theinsulating layer 209 so as to be adjacent to the TFT 21. An n+-typesemiconductor layer 211 that becomes a high-concentration, n-typeimpurity region is formed in a surface layer of the semiconductor layer210. A pattern of a bias line 12 is formed on the n+-type semiconductorlayer 211. A pattern of an electrode layer 212 is formed on the n+-typesemiconductor layer 211, including upper faces of the bias line 12 so asto be connected to the bias line 12. Also, a passivation layer 213 isdeposited on an entire surface, including the electrode layer 212 andthe insulating layer 209 on the TFT 21 side. Moreover, an adhesion layer214 having a flattened surface is formed so as to cover the passivationlayer 213, and a phosphor layer 215 as a wavelength conversion member isformed on the adhesive layer 214, thereby structuring the photoelectricconversion element 11. Note that an organic passivation layer made of PIor the like may be formed between the passivation layer 213 and theadhesion layer 214.

Here, let us consider the noises generated in the radiation imagepick-up device of this embodiment.

The noises which are generated when no electric charge amplification iscarried out within the pixel 6 depend on a kTC1 noise, a resistancenoise of the signal line 14 a, a parasitic capacity noise of the signalline 14 a, and a noise of the amplifier 15 a (including the gainswitching circuit 17). On the other hand, the noises which are generatedwhen the electric charge amplification is carried out within the pixel 6using the TFT 22 as the source follower circuit depend on the kTC1noise, and a noise of the source follower circuit. At this time, thenoise of the source follower circuit is very low in level. That is,higher sensitivity (S/N ratio) is obtained when the electric chargeamplification is carried out within the pixel 6 using the sourcefollower circuit rather than when no electric charge amplification iscarried out within the pixel 6.

Then, in the radiation image pick-up device of this embodiment, thesignal line is switched over to another one in correspondence to thesensitivity required for each photographing mode to take the X-rayphotograph. That is, any one of the signal lines 14 a and 14 b is freelyselectable in each pixel 6 in reading out a signal. The signal line 14 ais selected for the photographing mode involving a high dosage ofexposure to the X-rays, such as the still image photographing or anon-destructive inspection of the human body, and no electric chargeamplification is carried out within the pixel. On the other hand, thesignal line 14 b is selected for the photographing mode involving a lowdosage of exposure to the X-rays, such as the moving image photographingof the human body, and the electric charge amplification is carried outwithin the pixel using the source follower circuit.

A description will hereinafter be given to a specific photographingmethod employed when each signal line is selected.

(1) Photographing Mode Involving High Dosage of Exposure to X-Rays, Suchas Still Image Photographing or Non-Destructive Inspection

In this case, the signal line 14 a is selected in a manner as will bedescribed below, and no electric charge amplification is carried outwithin the pixel 6, and an output signal of the pixel 6 is read outthrough the signal line 14 a. Here, a capacity of the photoelectricconversion element 11 is assigned C1, a parasitic capacity of the signalline 14 a is assigned C2, and a capacity determined by capacities of thecapacitors Cf1, Cf2, and Cf3 of the amplifier 15 a is assigned Cf.

First of all, the TFTs 23, 26, 27, and 29 which are provided on thesignal line 14 b side are all turned OFF.

The X-ray applied to a subject for exposure is attenuated as it istransmitted through the subject to be wavelength-converted into visiblelight by the phosphor layer 215 as the wavelength conversion membershown in FIG. 4. The resultant visible light is then made incident onthe photoelectric conversion element 11 to be converted into electriccharges Q.

Subsequently, the TFTs 21 and 25 which are connected to the signal line14 a are both turned ON to set a gain of 1/Cf-fold in the amplifier 15a. As a result, the output voltage Vout is expressed by Vout=−Q/Cf.Then, the TFT 28 provided on the signal line 14 a side is turned ON,thereby reading out that output signal from the signal output circuit 3to the outside. After the output signal is read out, the TFT 24connected to the signal line 14 a is turned ON to remove the electriccharges still remaining in the photoelectric conversion element 11.Here, in the amplifier 15 a, a gain can be switched over to another onethrough the combination of the capacitors Cf1 to Cf3.

(2) Photographing Mode Involving Low Dosage of Exposure to X-Rays, Suchas Moving Image Photographing of Human Body

In this case, the signal line 14 b is selected in a manner as will bedescribed below, and the electric charge amplification is carried outwithin the pixel 6 to read out an output signal of the pixel 6 throughthe signal line 14 b. Here, a threshold voltage of the TFT 22 as thesource follower circuit is assigned Vth.

First of all, the TFTs 21, 24, 25, and 28 which are provided on thesignal line 14 a side are all turned OFF, while the TFT 23 connected tothe signal line 14 a is turned ON.

Similarly to the case of the still image photographing, the X-rayapplied to a subject for exposure is attenuated as it is transmittedthrough the subject to be wavelength-converted into visible light by thephosphor layer 215 as the wavelength conversion member shown in FIG. 4.The resultant visible light is then made incident on the photoelectricconversion element 11 to be converted into electric charges. Theresultant electric charges cause an electric potential fluctuation Vincorresponding to a quantity of incident light to the photoelectricconversion element 11 in a gate electrode of the TFT 22. Upon turn-ON ofthe TFT 22, an electric potential at a point C becomes (Vin−Vth) due tothis electric potential fluctuation Vin. In this case, for example, ifthe threshold voltage Vth is sufficiently small, then the signalobtained at the point C becomes a voltage signal which is substantiallyequal to the voltage signal Vin.

The TFTs 27 and 29 which are provided on the signal line 14 b side areboth turned ON, whereby the above voltage signal is read out from thesignal output circuit 3 to the outside through the amplifier 15 b. Afterthat voltage signal is read out, the TFT 26 connected to the signal line14 b is turned ON to remove the electric charges still remaining in thephotoelectric conversion element 11.

Note that, in this embodiment, when the electric charges still remainingin the photoelectric conversion element 11 are removed, the TFT 24 or 26is used. However, as in the prior art, an electric potential of the biasline 12 may be changed, or a voltage of the power supply 16 may bechanged.

As described above, according to this embodiment, there is realized theinexpensive and high-performance radiation image pick-up device which iscapable of freely switching sensitivity over to another one incorrespondence to a situation and an object of the photographing toflexibly cope therewith, i.e., capable of carrying out both the stillimage photographing and the moving image photographing for example whichare largely different from each other in dosage of exposure to theX-rays, and are also different in required sensitivity so as to meetthat request.

Note that while in this embodiment, a photoelectric conversion elementof a MIS type is adopted as the photoelectric conversion element 11,even when a photoelectric conversion element of a PIN type is adopted,the same effects can be obtained. Moreover, in this embodiment, therehas been exemplified the indirect type radiation image pick-up device inwhich the radiation is converted into the visible light in the phosphorlayer 215, and the resultant visible light is converted into theelectric charges in the photoelectric conversion element 11. However,even when the present invention is applied to a direct type radiationimage pick-up device, using a material such as amorphous selenium, inwhich the radiation can be directly converted into the electric charges,the same effects can be obtained.

Modification

In this embodiment, there is shown such a configuration that thescanning circuit 2 and the signal output circuit 3 are disposed onlyadjacent one sides of the sensor substrate 1, respectively. However, asshown in FIG. 5, the scanning circuit 2 and the signal output circuit 3may also be disposed on two sets of opposite sides of the sensorsubstrate 1, respectively. In this case, an effect that a driving speedis increased, and so forth is offered in addition to the effects of theabove-mentioned first embodiment. Hence, the more excellent radiationimage pick-up device can be realized.

Second Embodiment

Next, a radiation image pick-up device according to a second embodimentof the present invention will hereinafter be described.

The radiation image pick-up device of this embodiment has nearly thesame configuration as that of the radiation image pick-up device of thefirst embodiment but is different in that ICs of the signal outputcircuit is slightly different in configuration from those of the signaloutput circuit of the first embodiment.

FIG. 6 is an equivalent circuit diagram of the radiation image pick-updevice according to the second embodiment of the present invention, andFIG. 7 is an equivalent circuit diagram of one pixel and the signalreading circuit in this radiation image pick-up device. Note that theconstituent elements or the like corresponding to those of the firstembodiment are designated with the same reference numerals.

An IC 31 of the signal output circuit 3 of this radiation image pick-updevice, similarly to the case of the IC 5 of the first embodiment, isconnected to a pixel 6 through signal lines 14 a and 14 b. Unlike thefirst embodiment, however, the IC 31 has no amplifier 15 b, and thesignal lines 14 a and 14 b are connected to a common amplifier 15 a.

That is, in the IC 31, TFTs 24 and 25 are connected to the signal line14 a, and TFTs 26 and 27 are connected to the signal line 14 b. Also,the signal lines 14 a and 14 b are connected to each other through a TFT32 to be connected to one input terminal of the amplifier 15 a, and apower supply 16 is connected to the other input terminal of theamplifier 15 a. Moreover, a gain switching circuit 17 having capacitorsCf1, Cf2, and Cf3 is connected to the amplifier 15 a.

A description will hereinafter be given to a specific photographingmethod employed when each signal line is selected in this radiationimage pick-up device.

(1) Photographing Mode Involving High Dosage of Exposure to X-Rays, Suchas Still Image Photographing or Non-Destructive Inspection

In this case, the signal line 14 a is selected in a manner as will bedescribed below, and no electric charge amplification is carried outwithin the pixel 6, and an output signal of the pixel 6 is read outthrough the signal line 14 a. Here, a capacity of the photoelectricconversion element 11 is assigned C1, a parasitic capacity of the signalline 14 a is assigned C2, and a capacity determined by the capacitorsCf1, Cf2, and Cf3 of the photoelectric conversion element 11 is assignedCf.

First of all, the TFTs 23, 26, 27, and 32 which are provided on thesignal line 14 b side are all turned OFF.

The X-ray applied to a subject for exposure is attenuated as it istransmitted through the object to be wavelength-converted into visiblelight in the phosphor layer 215 as the wavelength conversion membershown in FIG. 4. The resultant visible light is then made incident onthe photoelectric conversion element 11 to be converted into electriccharges Q.

Subsequently, upon turn-ON of the TFTs 21 and 25 connected to the signalline 14 a, a gain of 1/Cf-fold is set in the amplifier 15 a. As aresult, an output voltage Vout is expressed by Vout=−Q/Cf. This voltagesignal is then read out from the signal output circuit 3 to the outside.After the voltage signal is read out, a TFT 24 connected to the signalline 14 a side is turned ON to remove the electric charges stillremaining in the photoelectric conversion element 11. Here, in theamplifier 15 a, a gain can be switched over to another one through thecombination of the capacitors Cf1 to Cf3.

(2) Photographing Mode Involving Low Dosage of Exposure to the X-Rays,Such as the Moving Image Photographing of Human Body.

In this case, the signal line 14 b is selected in a manner as will bedescribed below, and the electric charge amplification is carried outwithin the pixel 6, and an output signal of the pixel 6 is read outthrough the signal line 14 b. Here, a threshold voltage of the TFT 22connected to the signal line 14 b side is assigned Vth.

First of all, the TFTs 21, 24, and 25 which are connected to the signalline 14 a side are all turned OFF, while the TFT 23 connected to thesignal line 14 a side is turned ON.

Similarly to the case of the still image photographing, the X-rayapplied to a subject for exposure is attenuated as it is transmittedthrough the subject to be wavelength-converted into visible light in thephosphor layer 215 as the wavelength conversion member shown in FIG. 4.The resultant visible light is then made incident on the photoelectricconversion element 11 to be converted into electric charges Q. Theresultant electric charges Q cause an electric potential fluctuation Vincorresponding to a quality of incident light on the photoelectricconversion element 11 in a gate electrode of the TFT 22. Upon turn-ON ofthe TFT 22, a voltage at a point C becomes (Vin−Vth) due to the electricpotential fluctuation. For example, if the threshold voltage Vth issufficiently small, then the voltage signal at the point C becomes avoltage signal which is substantially equal to the electric potentialfluctuation Vin.

Upon turn-ON of the TFT 27 connected to the signal line 14 b side, theelectric charges are accumulated in the capacitor C3. In this state,upon turn-ON of the TFT 32, a gain of 1/Cf-fold is set in the amplifier15 a. As a result, an output voltage Vout is expressed by Vout=−Q/Cf.This voltage signal is then read out from the signal output circuit 3 tothe outside through the amplifier 15 a. After the voltage signal is readout, the TFT 26 connected to the signal line 14 b is turned ON to removethe electric charges still remaining in the photoelectric conversionelement 11.

In this embodiment, in the amplifier 15 a, the gain can be switched overto another one through the combination of the capacitors Cf1 to Cf3.Hence, unlike the case where the electric charge amplification iscarried out within the pixel 6 in the first embodiment, a magnitude ofthe output signal can also be selected.

Note that while when the electric charges still remaining in thephotoelectric conversion element 11 are removed, the TFT 24 or 26 isused, an electric potential of the bias line 12 may be changed, or avoltage of the power supply 16 may also be changed as in the prior art.In addition, in this embodiment as well, similarly to the change of thefirst embodiment, the scanning circuit 2 and the signal output circuit 3may also be suitably provided in two sets of opposite sides of thesensor substrate 1, respectively.

Moreover, in the first and second embodiments, there have been describedthe example in which a consideration is given to the still imagephotographing (non-destructive inspection) and the moving imagephotographing as the photographing modes, and the two signal lines 14 aand 14 b are distributed for each pixel 6 so as for any one thereof tobe freely selectable. However, it is also possible that three or moresignal lines are distributed for each pixel in order to more finely copewith the photographing corresponding to the various kinds ofphotographing modes.

Third Embodiment

Next, a third embodiment of the present invention will hereinafter bedescribed.

This embodiment discloses herein a radiation image pick-up systemincluding the radiation image pick-up device described in the secondembodiment of the first and second embodiments. Of course, the radiationimage pick-up device described in the first embodiment can also beapplied to this radiation image pick-up system. Note that theconstituent elements or the like corresponding to those of the first andsecond embodiments are designated with the same reference numerals.

FIG. 8 is a schematic block diagram schematically showing the radiationimage pick-up system according to the third embodiment of the presentinvention, FIG. 9 is a flow chart showing an operation of the radiationimage pick-up system, and FIG. 10 is a timing chart of an image pick-upoperation using the radiation image pick-up system.

As shown in FIG. 8, the radiation image pick-up system includes theradiation image pick-up device 41 described in the second embodiment, adrive unit 42 for driving the radiation image pick-up device 41, anX-ray generation unit 43 for applying radiation, i.e., an X-ray in thiscase to an subject, an image pick-up switch 44 with which any one of thesignal lines 14 a and 14 b is freely selectable by an operator, aphotographing mode selection unit 45 for outputting an electrical signalrepresenting that any one of the signal lines 14 a and 14 b is selectedbased on an input to the image pick-up switch 44, and a control unit 46for controlling operations of the X-ray generation unit 43 and the driveunit 42 based on the electrical signal sent from the photographing modeselection unit 45.

The selection of the image pick-up mode can be carried out with theimage pick-up switch 44, which is adapted to be switched ON into strokescorresponding to the number of signal lines 14 a and 14 b, i.e., intotwo strokes in this case. The strokes correspond to an increase in adosage in ascending order. In a state in which a switch 44 a is switchedON into the first stroke, the moving image mode is selected, while in astate in which a switch 44 b is switched ON into the second stroke, thestill image mode is selected. Note that it is configured such that whenthe switch 44 b is switched ON into the second stroke, the switch 44 ais also switched ON simultaneously into the first stroke. Since thephotographing is repeatedly carried out by continuing to switch ON theimage pick-up switch 44, for example, the switch 44 b of the imagepick-up switch 44 is switched ON into the second stroke during thephotographing of the moving image, thereby allowing the still image tobe photographed. For end of the photographing, the image pick-up switch44 has to be switched OFF (a state of the switching-OFF has to beprovided for the image pick-up switch 44).

Here, a description will hereinafter be given to the control for thedosage of the X-rays in the X-ray generation unit 43 made by the controlunit 46.

In case of the still image mode, there is generated a relatively highdosage of X-rays used to take an X-ray photograph of the breast throughthe still image photographing or the like. On the other hand, in case ofthe moving image mode, since a subject (patient) is irradiated with theX-rays for a long period of time, in this case, a low dosage ofpulse-like X-rays is generated.

In addition, as described in the second embodiment, the drive unit 46controls the radiation image pick-up device 41 such that in the case ofthe still image photographing, no electric charge amplification iscarried out within the pixel, and the output signal is read out to theoutside through the signal line 14 a, while in the case of the movingimage photographing, the electric charge amplification is carried outwithin the pixel using the source follower circuit, and the outputsignal is read out to the outside through the signal line 14 b.

In the radiation image pick-up system according to this embodiment, asshown in FIG. 9, first of all, a photographing mode is selected by anoperator (Step S1). That is, when the switch 44 a or 44 b of thephotographing switch 44 is switched ON into the first or second stroke,the photographing mode is selected by the photographing mode selectionunit 45. Subsequently, when the moving image mode is selected, theapplication of the X-rays corresponding to the moving image by the X-raygeneration unit 43 is started (Step S2) and the control for theradiation image pick-up device 41 through the drive circuit 42 isstarted (Step S3) by the control unit 46 to carry out the moving imagephotographing (Step S4). On the other hand, when the still image mode isselected, the application of the X-rays corresponding to the still imageby the X-ray generation unit 43 is started (Step S5) and the control forthe radiation image pick-up device 41 through the drive circuit 42 isstarted (Step S6) by the control unit 46 to carry out the still imagephotographing (Step S7).

Then, in Step S8, when the photographing is further continued to becarried out, in the case of the moving image photographing, the switch44 a of the photographing switch 44 is continued to be switched ON intothe first stroke, while in the case of the still image photographing,the switch 44 b of the photographing switch 44 is continued to beswitched ON into the second stroke. When the photographing is intendedto come to an end, the photographing switch 44 is just switched OFF.

Subsequently, with reference to FIG. 10, a description will hereinafterbe given to an operation of the radiation image pick-up device when thephotographing proceeds from the moving image photographing to the stillimage photographing.

When the switch 44 a of the photographing switch 44 is switched ON intothe first stroke to select the moving image mode, a photographing signalis inputted to the radiation image pick-up device 41. Subsequently, theTFT 23 is turned ON by the drive unit 42, and the TFTS 26 and 22 arethen turned ON, thereby resetting the circuit. Subsequently, the X-rayapplied from the X-ray generation unit 43 to a subject is attenuated asit is transmitted through the subject to be wavelength-converted intovisible light in the phosphor layer 215 as the wavelength conversionmember shown in FIG. 4. The resultant visible light is made incident onthe photoelectric conversion element 11 to be converted into electriccharges Q. The resultant electric charges Q cause the electric potentialfluctuation Vin corresponding to a quantity of incident light to thephotoelectric conversion element 11 in the gate electrode of the TFT 22.The TFT 22 is turned ON due to that electric potential fluctuation Vinto accumulate the electric charges in the capacitor C2′. Subsequently,the TFT 27 is turned ON to accumulate the electric charges in thecapacitor C3. Upon turn-On of the TFT 32, the output signalcorresponding to the electric charges accumulated in the capacitor C3 isread out from the signal output circuit 3 to the outside. Then, whilethe switch 44 a of the photographing switch 44 is switched ON into thefirst stroke, the moving image photographing is continuously repeated.

At this time, when the switch 44 b of the photographing switch 44 isswitched ON into the second stroke, the photographing proceeds to thestill image photographing. In the case of the still image photographing,first of all, the TFTs 23, 22, 26, 27, and 32 which are provided on thesignal line 14 b side are all turned OFF. However, the photographingswitch 44 may be switched ON at various timings such as a timing duringthe application of the X-rays, and a timing during the reading of theoutput signal. Thus, the TFTs 21 and 24 are turned ON right before thestill image photographing, thereby resetting the circuit. Subsequently,the X-ray applied from the X-ray generation unit 43 to a subject isattenuated as it is transmitted through the subject to bewavelength-converted into visible light in the phosphor layer 215 as thewavelength conversion member shown in FIG. 4. The resultant visiblelight is made incident on the photoelectric conversion element 11 to beconverted into electric charges Q. The resultant electric charges Q areaccumulated in the capacitor C2 by turning ON the TFT 21. Subsequently,upon turn-ON of the TFT 25, the output signal corresponding to theelectric charges Q accumulated in the capacitor C2 is read from thesignal output circuit 3 to the outside through the amplifier 15 a. Notethat while essentially, the output signal Vout is expressed byVout=−Q/Cf, in FIG. 10, the polarity of the output signal Vout isinverted to be expressed as plus (+).

As described above, according to this embodiment, there is realized theinexpensive and high-performance radiation image pick-up system which iscapable of freely switching sensitivity over to another one incorrespondence to a situation and an object of the image photographingto flexibly cope therewith, i.e., capable of carrying out both stillimage photographing and moving image photographing for example which arelargely different from each other in dosage of exposure to the X-raysand which are also different in required sensitivity so as to meet thatrequest.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the claims.

1. A radiation image pick up device comprising: a pixel including aconversion element for converting incident radiation into an electriccharge and first and second semiconductor elements for transferring asignal charge corresponding to the electric charge converted by theconversion element for storage or further processing; and a scanningcircuit for independently selecting the first and second semiconductorelement.
 2. A radiation image pick up device according to claim 1,wherein either of the first semiconductor element and the secondsemiconductor element is a source follower.
 3. A radiation image pick updevice according to claim 1, wherein the second semiconductor element isa source follower, and wherein the first semiconductor element isselected for a first dosage of the radiation, and the secondsemiconductor element is selected for a second dosage of the radiation,wherein the first dosage of the radiation is larger than the seconddosage of the radiation.
 4. A radiation image pick up device accordingto claim 1, further comprising: a first signal wiring, through which thefirst semiconductor element transfers the signal charge; a second signalwiring, through which the second semiconductor element transfers thesignal charge; and a signal read-out circuit for reading the signalcharge through the first or second signal wiring.
 5. A radiation imagepick up device according to claim 4, wherein the signal read-out circuithas a first amplifier connected electrically to the first signal wiringand a second amplifier connected electrically to the second signalwiring.
 6. A radiation image pick up device according to claim 4,wherein the signal read-out circuit has an amplifier connectedelectrically to the first signal wiring and the second signal wiringcommonly, and has a gain switchable between at least two gain values. 7.A radiation image pick up device according to claim 1, furthercomprising a wavelength converter for converting a wavelength of theradiation into one which can be sensed by the conversion element.
 8. Aradiation image pick up system comprising: a radiation image pick updevice according to claim 1; a selection unit for selecting any one of aplurality of radiographing modes of said radiation image pick-up deviceaccording to a magnitude of dosage of the radiation.
 9. A sensorsubstrate for use in a radiation image pick-up device having a scanningcircuit, comprising: a pixel including a conversion element forconverting incident radiation into an electric charge and first andsecond semiconductor elements for transferring a signal chargecorresponding to the electric charge converted by the conversion elementfor storage or further processing; and a scanning circuit forindependently selecting the first and second semiconductor element. 10.A radiation image pick up device according to claim 1, comprising asensor substrate, wherein the sensor substrate includes the pixel.
 11. Aradiation image pick up device comprising: a pixel including aconversion element for converting incident radiation into an electriccharge and first and second semiconductor elements, said firstsemiconductor element for transferring a signal charge corresponding tothe electric charge converted by the conversion element for storage orfurther processing without use of said second semiconductor element, andsaid second semiconductor element for transferring a signal chargecorresponding to the electric charge converted by the conversion elementfor storage or further processing without use of said firstsemiconductor element; and a scanning circuit for independentlyselecting the first and second semiconductor element.